1. Field of the Invention
The present invention relates to 3,6-anhydro-L-galactose dehydrogenase which produces a novel 3,6-anhydrogalatonic acid by metabolizing 3,6-anhydro-L-galactose as a bio energy production technology.
2. Discussion of Related Art
The world is currently facing depletion and rises in prices of petroleum resources, which are a major energy resource, and environmental issues such as global warming derived from an increase of carbon dioxide in the atmosphere by an excessive use of fossil fuels. Therefore, there is an urgent need for the development of a new alternative energy resource which can reduce carbon dioxide emissions. As a major alternative energy, bio-energy in which renewable and abundant plant-based biomass is used as a raw material is being spotlighted. Compared with other alternative energies, bio-ethanol is currently in high demand since it can be used as transportation fuel. Many countries including the United States and Brazil recommend the use of bio-ethanol, which is required by law.
As a first generation biomass currently used for producing bio-ethanol, a sugar-based biomass and a starch-based biomass derived from food resources have a lot of problems in that the use of resources for food causes rising grain prices. In order to overcome such a problem, research on a second generation biomass (ligneous biomass) for energy production is underway. However, a ligneous biomass includes a large amount of lignin, which is a non-biodegradable substance, and therefore ligneous biomass is hardly converted into fermentable monosaccharides. A third generation biomass (marine algae biomass) has advantages in that there is no competition with food resources and it is easily converted into fermentable sugars due to an absence or low content of lignin. Accordingly, the marine algae as a next generation bio-energy source is receiving attention and bio-energy production technologies using the marine algae are being studied actively. In particular, South Korea is surrounded by water on three sides, has rich marine resources, and hence is suitable for using the marine algae as biological resources. Further, South Korea is one of the top ranking global marine algae producing countries along with China, Japan, and North Korea with its annual gross product amounting to 13,754 tons as of 2006. However, there is still room for improvement in terms of utilization thereof (Fisheries Production Statistics, 2006, Agriculture and Fisheries Production Statistics Division, Population and Social Statistics Bureau, National Statistical Office, Korea).
Out of well-known marine algae, research on red algae (for example, Gelidium amansii) as a source material is being studied especially actively. More than 70% of the total dry weight of the red algae is polysaccharides capable of being converted into fermentable sugars to be used for microorganisms. A main component of the polysaccharides derived from the red algae biomass is agar with about 60% of total dry weight, and thus agar is considered as a main source for bio-energy production.
Agar is a linear polysaccharide in which 3,6-anhydro-L-galactose (hereinafter referred to as ‘L-AHG’) and D-galactose (hereinafter referred to as ‘D-Gal’) are linked together alternately in an α-1,3-glycosidic bond and a β-1,4-glycosidic bond, and is a main component of cell walls in the red algae. Agar includes agaropectin and agarose. Agaropectin has a same basic structure as agarose but differs from agarose in that it has substituent groups such as a sulfate group, pyruvic acid, and glucuronic acid (Carbohydrate Research (1971) 16:435-445).
Up to now, different types of microorganisms which can decompose agar have been identified. Among them, Saccharophagus degradans 2-40 (hereinafter referred to as ‘S. degradans’), which was first isolated in Chesapeake Bay in Virginia, USA, is a rod-shaped, aerobic marine microorganism, and a complete genome sequence thereof has been reported. S. degradans can decompose at least 10 or more complex polysaccharides, including agar, and has an agar catabolic system which allows agar to be used in metabolic processes. Enzymes used in the agar catabolic system are divided into four groups: GH16, GH50, GH86, and GH117. The groups other than GH117 are estimated as β-agarase, and an Aga50D enzyme belonging to the GH50 group has been reported to produce neoagarobiose (hereinafter referred to as ‘NA2’), which is a disaccharide, as a final product (Appl Micro boil Biotechnol 86:227-234, 2010). Moreover, reports have revealed that neoagarobiose hydrolysis enzyme (hereinafter referred to as ‘NABH’) belonging to the GH117 group cuts an α-1,3-bond of NA2 (disaccharide). Microorganisms that metabolize agar can convert agar into a fermentable sugar, D-Gal, and a non-fermentable sugar, L-AHG, using agarase. In order to produce bio-energy using the marine algae, pre-treatments are essential so as to convert the marine algae into fermentable sugars. However, L-AHG (monosaccharide) produced in the metabolic process is not used as a fermentable sugar in general microorganisms, thereby decreasing production yield of bio-energy. Furthermore, a metabolic pathway of D-Gal in many types of microorganisms is well known but research on L-AHG metabolic processes in the microorganisms which use agar as a carbon source has not been reported. As a result, in order to produce bio-energy using L-AHG, research on L-AHG metabolic process of the microorganisms which use agar as a carbon source is required to know an accurate metabolic pathway.